Interpretive Summary: Penland's beardtongue is a very rare snapdragon that occurs in only one county in central Colorado. The species is listed as endangered under the Endangered Species Act. Its continued existence depends critically on being able to produce sufficient fruit and seed so that new individuals will be available in the future to replace adults in current populations when they die. Most rare plants produce fruits and seeds only with the help of flower-visiting pollinators such as native bees. When pollinators are required for rare plants to reproduce sexually, they must also be protected by land managers responsible for preserving plants. We studied the reproductive biology and pollinators of Penland's beardtongue to determine whether flowers set fruit without being visited by pollinators,and to learn what those pollinators might be. We learned that plants reproduce only minimally in the absence of pollinators, and that the important pollinators are several species of megachilid bees in the genus Osmia, and bumblebees. If Penland's beardtongue is to be preserved then its pollinators must also be encouraged to thrive. Because of the complexity of the pollination system in which it is embedded, this plant is best preserved by applying principles of ecosystem conservation.

Technical Abstract:
Abstract: Penbland's beardtongue, a rare endemic plant of the Colorado Plateau, displays a mixed breeding system. Plants are partially self-compatible but set more fruits when cross-pollinated than when self-pollinated. Fruit production is significantly increased by pollinators. However, in two years study there was no indication that fruit set was being limited by inadequate pollinator visitation. Pollinator effectiveness was judged by correlating bee behavior at the flowers with analysis of the pollen carried on bee bodies. The most important pollinators were native megachilid bees, particularly in the genus Osmia. The bee pollinators of Penland's beardtongue are essential to its reproduction and must be preserved along with this rare plant.